Belt Grinder belt speed question

R

Ryan J

Joined
Jul 14, 2014
Messages
233
Making progress on my belt grinder. I'm wondering at what speed you guys grind for stock removal. Ive searched around but haven't found much. Most of the threads pertained to sharpening and the one thread I found the guy was running 7200 fpm and Im not sure I have the hp for that.

The motor Im using is a 2 hp 6000 rpm and already has a 2.5 drive wheel on the shaft. This will give me a belt speed of 3930 fpm. Is this fast enough or do I need to go with a bigger drive wheel?
 
6000 rpm? That is wicked fast. What kind of motor? Do you have a picture of the motor plate with the specs?
 
As an FYI, the kmg is about 3600 sfpm with 4" wheel. Other grinders run from 4400 to 5400. These are other well known grinders that are plug and play. I won't mention names since I am going from memory and don't want sart a pissing match. I think your target sfpm is a good place to start. I'm guessing this is not a 3 phase motor?
 
I was being a little conservative because I dont want to max the motor out. DC motor.

I looked at the kmg specs. Then I seen others running over 6000 so I wondered if 4000 was fast enough.
Thanks for the reply. I'll go with it like it is.
 
That is a DC open frame motor ( probably from a treadmill). It is a very poor choice for a grinder motor. Both the HP and the speed ratings are misleading.

The HP on those things is "Rated HP", similar to 3HP routers and 5HP vacuums. The plate says it would "develop" 2HP with the motor running at 6100RPM and at 130VDC. In actuality, that's not going to happen. The speed is the max attainable speed with no load on those DC motors...not what they will run at normally. It is probably closer to 1HP in actual power, which would be fine for running your grinder build......but still a poor choice for a grinder because of the frame type.BTW, you will have to use a 110VAC/130VDC variable speed controller ( maybe you can salvage the one that came with the tread mill) to run the motor.
 
Thanks Stacy. Yeah Ive read your recommendations on treadmill motors elsewhere on here. I know its not ideal it's what I have. It will be better then no grinder at all untill I can get a better motor. At least it draws 15 amps instead of 10 like some of them so should be okay on power like you say. One post you had a numbered list of deficiencies of treadmill motors and Im addressing all of them. Right now Im building a control panel enclosure to seal off the circuitry. And I have a plan to protect and cool the motor. I have the pulse modulator from the treadmill. Thanks for the info on the drawbacks so I can address them.
 
Ryan - one thing to consider since you've got a DC motor for variable speed, the max speed is mostly for profiling a blade. I think you'll find a LOTS of grinding work will be done at much slower speeds, even down to 1,000 SFM. Much better control down slow. An easy thumbnail belt SFPM speed is the RPM of a 4" drive pulley will be just a tad slower than the actual belt speed in SFPM. In fact, a 3.8" diameter drive pulley will just about have drive wheel RPM equaling SFPM.

4,000 SFPM belt speed will really throw some sparks in grinding.

Ken H>
 
Ken H> said:
Ryan - one thing to consider since you've got a DC motor for variable speed, the max speed is mostly for profiling a blade. I think you'll find a LOTS of grinding work will be done at much slower speeds, even down to 1,000 SFM. Much better control down slow. An easy thumbnail belt SFPM speed is the RPM of a 4" drive pulley will be just a tad slower than the actual belt speed in SFPM. In fact, a 3.8" diameter drive pulley will just about have drive wheel RPM equaling SFPM.

4,000 SFPM belt speed will really throw some sparks in grinding.

Ken H>
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Glad to hear it'll throw some sparks! I've read on hear that high rpms destroys the finer belts. Thats one of the advantages Ill have. The ratios will be a little different then you stated because Im incorporating a jack shaft with pillow blocks to reduce side loading on the motor. Going to cut a V groove in the attached flywheel for a belt. Cant remember the numbers but I plugged it all into onljne calculators. I think it was a 6" drive and 4" driven will give me around 4000 fpm. Ill figure that part out again when its time to buy the pulleys. Right now its wiring and building the control box. I got lucky with this unit because the speed sensor that gives people fits is in no way connected to any of the circuitry involved in motor control. It runs to the odometer calorie counter and thats it. So I dont need it which is great. That is unless I feel I need to keep track of calories burned while grinding
 
Ryan - Not knowing what your final motor RPM's will be, the numbers I mentioned are "drive pulley" (better said as drive wheel), I"m guessing this is the jack shaft RPM also.

4,000 SFPM is plenty fast for grinding - I understand the need to use the DC motor on hand, but a drive drive is so much smoother than a shaft drive setup. Of course, how smooth the shaft drive is depends a great deal on quality of pulleys.

Good luck with your grinder - they are NICE.

Ken H>
 
Ryan, Before you spend a lot of time making a treadmill motor work take a look on Ebay and also look at electric motor suppliers for a more suitable motor. You should be able to find a nice 1 1/2 or 2 hp TEFC (totally enclosed Fan cooled) 3 phase motor used or even new for a good price. Look for a model with a mounting foot for use with pulleys or a C face motor that can be mounted direct drive. Motors last a long time so buying a used motor is sometimes a good deal. I sold a 1 1/2 3 phase last year for $89 + shipping that was only a year old because I wanted a 2 hp motor. The motor you choose will be very important to the performance of your grinder IMHO. If you are serious about grinding blades then a few more bucks spent on a good motor will be money well spent. Search motors on Blade Forums and see what others have to say about motor selection. Larry
 
Ken you have me reconsidering my build. Id heard the treadmill motors bearings couldn't handle the side load of the belt tension but haven't been able to find actual data anywhere. I know it already had a good amount of side load from the drive belt in the treadmill. It would save a lot of money. The build was about $80 because of the pulleys, pillow blocks, and shafts. My Idlers come in a pack of 4 so O could convert one to a drive wheel. And they're three inches so belt speed would be 4739 fpm so no worries about being fast enough. And Larry Ill keep your post in mind when it comes time to replace the motor. Right now Im buying a house, have a young son, and my construction business can get slow in the winter so I have about $0 to spare. As far as the work it takes I enjoy it and all the extra retrofitting due to the treadmill is done already. When I need to replace the motor it will be a simple deal. It's not that Im not serious or am trying to cut corners. I'm just doing what I have to do with what I have. I know treadmill is a bad word around here and it's not the best option but hey, its a $25 2x72.
 
Ryan J said:
Ken you have me reconsidering my build. Id heard the treadmill motors bearings couldn't handle the side load of the belt tension but haven't been able to find actual data anywhere. I know it already had a good amount of side load from the drive belt in the treadmill. It would save a lot of money. The build was about $80 because of the pulleys, pillow blocks, and shafts. My Idlers come in a pack of 4 so O could convert one to a drive wheel. And they're three inches so belt speed would be 4739 fpm so no worries about being fast enough. And Larry Ill keep your post in mind when it comes time to replace the motor. Right now Im buying a house, have a young son, and my construction business can get slow in the winter so I have about $0 to spare. As far as the work it takes I enjoy it and all the extra retrofitting due to the treadmill is done already. When I need to replace the motor it will be a simple deal. It's not that Im not serious or am trying to cut corners. I'm just doing what I have to do with what I have. I know treadmill is a bad word around here and it's not the best option but hey, its a $25 2x72.
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Do what you do brother, and all will fall into place in the long run. One thing that I find admirable about people is their ingenuity, the ability to utilize/build that which they need in order to accomplish a task. Making suggestions on things that require disposable income are easy to do from afar, so I won't kick that dead horse any dead'r. Treadmill motors are not an original idea when it comes to grinders; that notion alone suggests that someone out there uses one on his/her grinder... there might even be a second out there as well....

I built a grinder the other night that would cause most grinder aficionados vomit... cost me a 3" section of scrap I-beam and a 5/16th bolt.... and it works like a charm!!! :D

IMG_0134_zps514c3f44.jpg


IMG_0136_zps9ce5fbc4.jpg
 
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SinePari said:
Do what you do brother, and all will fall into place in the long run. One thing that I find admirable about people is their ingenuity, the ability to utilize/build that which they need in order to accomplish a task. Making suggestions on things that require disposable income are easy to do from afar, so I won't kick that dead horse any dead'r. Treadmill motors are not an original idea when it comes to grinders; that notion alone suggests that someone out there uses one on his/her grinder... there might even be a second out there as well....

I built a grinder the other night that would cause most grinder aficionados vomit... cost me a 3" section of scrap I-beam and a 5/16th bolt.... and it works like a charm!!! :D

IMG_0134_zps514c3f44.jpg


IMG_0136_zps9ce5fbc4.jpg
Click to expand...

Think about that...the whole grinder is suspended on a 5/16" bolt. I can bend a 5/16" bolt in my hand. Glad you are being ingenuitive, but that looks like an accident waiting to happen.
 
OMG, I'm a safety guy by profession, and that will give me nightmares for a week, lol
 
Stacy E. Apelt - Bladesmith said:
Think about that...the whole grinder is suspended on a 5/16" bolt. I can bend a 5/16" bolt in my hand. Glad you are being ingenuitive, but that looks like an accident waiting to happen.
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It's a Grade 8 bolt, and the filler is 12018... There is also 2 nuts to ensure a tight connection.... I'm not an engineer by trade, but I'm pretty sure it'll hold true... :D



... pretty sure..... lol



While the weld deposit does take away from the sheer strength properties of the G8 hardware, there should be no such thing as catastrophic failure... that is unless someone takes a cross-peen to it while grinding. A safer means of fabrication would be drilling 5/16th through the section, threading the bolt through, and welding the bolt to the underside... better?, well maybe.
 
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Take a 1/2" pipe and put over the bolt with it supporting grinder. This would provide a extra support - but just what size grinder is that anyway? A 4" disk? 7" disk? 10"?

A 4" isn't that hard to support.

Ken
 
Ken H> said:
Take a 1/2" pipe and put over the bolt with it supporting grinder. This would provide a extra support - but just what size grinder is that anyway? A 4" disk? 7" disk? 10"?

A 4" isn't that hard to support.

Ken
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It's a 4-1/2" with a 7" flap-wheel... Not a bad idea at all, because that 1/2" pipe would closely mimic the meat of the handle, which nobody second guesses when it comes to safety...

canid said:
I'm a reckless guy by profession and that makes me uncomfortable to see also.
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lol, you guys are killing me!!! :D



In an effort not to derail the OP; His use of a treadmill motor doesn't seem like a bad idea after all, now does it? :D
 
No worries about derailment. I got the info I came for. Have to admit you have a point about no one ever questioning the integrity of the factory handle. If you clamped the handle in the vice nobody would bat an eye. And that's a just a bolt the exact same diameter but shorter and ungraded with some rubber and plastic around it. And we trust that to use to push and pull on the grinder.
 
SinePari said:
It's a 4-1/2" with a 7" flap-wheel... Not a bad idea at all, because that 1/2" pipe would closely mimic the meat of the handle, which nobody second guesses when it comes to safety...



lol, you guys are killing me!!! :D



In an effort not to derail the OP; His use of a treadmill motor doesn't seem like a bad idea after all, now does it? :D
Click to expand...

What is the max speed on the 7" flap? Check the label and please report back. What is the speed of the 4.5" grinder?
 
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